[El Gato]

I've been working on verb conjugation. I started with the present tense, then the preterite and am now on the imperfect. I'm starting to notice the conjugations in those tenses when I read Spanish.

But I've also noticed mixed in some sentences with conjugated verbs are others that are left unconjugated. Is there a reason some verbs are conjugated and others are not?

For example:
Vamos a pasar el mes de enero en el sur.

"Pasar", spend, is left unconjugated. I noticed several other sentences like this.